The strutucre of fimbrin, one of the members of a family of actin cross-linking proteins, is currently being examined by synchrotron crystallography. Fimbrin binds and cross-links filamentous actin, contributing to cytoskeletal structure and function. Fimbrin contains a calcium binding domain as well as two actin binding domains. Two actin binding domains of fimbrin have been crystallized and the strutucre will be solved using multiple isormorphous replacement. These crystals diffract to about 2.5 angstroms. To date, diffraction data has been obtained from the native crystal as well as from two heavy atom derivatives. Preliminary protein electron density maps, calculated from the diffraction data, show alpha helics to be a predominant secondary structural feature of fimbrin. Ultimately, to improve this protein map it will be necessary to collect data from the heavy atom derivatives to higher resolution.